Euclidean Q-balls of fluctuating SDW/CDW in the 'nested' Hubbard model of high-T$_c$ superconductors as the origin of pseudogap and superconducting behaviors

TL;DR

This paper proposes that Euclidean Q-balls formed from spin and charge fluctuations in the nested Hubbard model explain the pseudogap phase and superconducting behaviors in high-Tc cuprates, linking theoretical predictions to experimental observations.

Contribution

It introduces a novel Euclidean Q-ball framework for understanding pseudogap and superconductivity, with analytical solutions and experimental correlations.

Findings

Q-balls form below temperature T* with finite condensate density.

Q-balls expand to infinity at the superconducting transition temperature Tc.

The theory explains experimental dependencies of Tc and magnetic properties in cuprates.

Abstract

The origin of the pseudogap (PG) phase and superconducting behaviors in high-Tc superconductors is proposed, based on the picture of Euclidean Q-balls formation, that carry Cooper/local-pair condensates inside their volumes. Unlike the baryonic Q-balls in supersymmetric standard model, the Euclidean Q-balls describe spin-/charge densities, that oscillate in Matsubara time, and are found in the 'nested' repulsive Hubbard model of high-Tc superconductors. Euclidean Q-balls arise due to global invariance of the effective theory under the phase rotation of the Fourier amplitudes of spin-/charge fluctuations, leading to conservation of the 'Noether charge' Q in Matsubara time. Due to local minimum of their potential energy at finite amplitude of the density fluctuations, the Q-balls provide greater binding energy of fermions into local/Cooper pairs than an exchange with infinitesimal lattice/charge/spin quasiparticles in the usual Frohlich mechanism. We show that below some temperature T* the Q-balls arise with a finite density of superconducting condensate inside them. The Q-balls expand their sizes to infinity at superconducting transition temperature Tc. Fermionic spectral gap inside the Q-balls arises in the vicinity of the 'nested' regions of the bare Fermi surface. Solutions are found analytically from the Eliashberg like equations with the 'nesting' wave vectors connecting different 'hot spots' on the bare Fermi surface. The experimental dependences of Uemura (1989) of Tc on superconducting density n_s, as well as of Li et al. (2010) of diamagnetic moment on magnetic field above Tc in cuprates follow naturally from the proposed theory. The 'breathing modes' of the Q-balls in Matsubara time, as well as sharp maximum in specific heat temperature dependence in the vicinity of the 1-st order phase transition into Q-balls gas phase are also predicted.